1. Technical Field
The present invention relates to a method of checking an installed state of a jet pump beam and, in particular, to a method of checking an installed state of a jet pump beam suitable for applying to a jet pump provided in a reactor pressure vessel in a boiling water reactor.
2. Background Art
A boiling water reactor is provided with a plurality of jet pumps disposed in a downcomer which is an annular region formed between a reactor pressure vessel (hereinafter, referred to as a RPV) to which a recirculation pipe is connected and a cylindrical core shroud surrounding a core in the RPV. The jet pump includes an elbow, a nozzle, a bell mouth, a throat, and a diffuser. Cooling water pressurized by drive of a recirculation pump installed to the recirculation pipe flows through the recirculation pipe, and as driving water, passes through a riser pipe, a transition piece, and the elbow, and is ejected from the nozzle into the bell mouth and the throat. The nozzle increases the speed of the driving water. The cooling water around the nozzle in the downcomer is sucked into the throat as suction water by action of the ejected driving water, and flows into the diffuser while exchanging kinetic momentum with the driving water. The cooling water discharged from the diffuser is supplied to the core through a lower plenum in the RPV.
The elbow, the nozzle, the bell mouth, and the throat included in the jet pump installed in the reactor pressure vessel are joined together as a single-piece construction and constitute a removable inlet mixer. At the time of inspection and repair, the inlet mixer is removed from a transition piece and the diffuser.
The driving water flowed upward in the riser pipe changes its flowing direction 180° in the elbow and flows into the nozzle of the jet pump as a downward flow. Consequently, since upward force exerted by a flowing fluid is applied to the elbow, a top surface of the elbow is held down by a jet pump beam. Either end of the jet pump beam is inserted into a groove formed in each of a pair of projecting portions extending upward from the transition piece connected to the top of the riser pipe, and the jet pump beam is kept in a deflection state, that is, an arched state.
Japanese Patent Laid-open No. 63(1988)-168594 states a jet pump for a boiling water reactor. This jet pump is provided with a riser pipe, an inlet mixer, and a diffuser. The inlet mixer has an elbow communicated with the riser pipe, a nozzle connected to the elbow, a bell mouth disposed below the nozzle, and a throat provided to a lower end of the bell mouth. A transition piece having a pair of projecting portions is connected to the riser pipe, and the elbow is disposed between the projecting portions. A jet pump beam is inserted to each groove formed in the pair of projecting portions. A tensioner disposed between the jet pump beam and the top portion of the elbow adds a deflection amount δ to the jet pump beam. In this way, the elbow is installed to the transition piece, and the elbow is pushed against the transition piece by the jet pump beam having the deflection amount δ.
Japanese Patent No. 4052377 states a method of installing a jet pump beam using a jet pump beam fixing apparatus. This jet pump beam fixing apparatus has a fixing device attached to a jet pump beam. The fixing device engages with ratchet teeth formed around a beam bolt which engages with a jet pump beam to fix the jet pump beam. In the conventional method of installing the jet pump beam stated in Japanese Patent No. 4052377, the jet pump beam, each groove formed in a pair of projection portions installed on a transition piece, and a top surface of an insert member fitted into a recess formed in a top portion of an elbow where a lower end portion of the beam bolt installed to the jet pump beam comes in contact with, are checked for the presence of a foreign object, and when the foreign object is found, it is removed. Then, the jet pump beam is inserted into each groove formed in a pair of projecting portions facing each other of the transition piece, the center portion of the jet pump beam is pulled up with a tensioner to add a predetermined bent amount to the jet pump beam, and the beam bolt is tightened by the above fixing device.
Japanese Patent Laid-open No. 2010-14674 states a method of installing a jet pump beam using a bolt fixing apparatus for a jet pump beam. This bolt fixing apparatus has a lock cap slidable in the axial direction, provided to the beam bolt, and a body housing for accommodating the lock cap, installed on the upper surface of the jet pump beam. In the bolt fixing apparatus, tapered external teeth are formed on an outer circumferential surface of the lock cap and internal toothed grooves that engage with the tapered external teeth are formed in the body housing. In Japanese Patent Laid-open No. 2010-14674, the jet pump beam is installed as follows: The jet pump beam is inserted into each groove formed in a pair of projecting portions facing each other of a transition piece, and the beam bolt rotatably installed to the jet pump beam pushes an elbow of an inlet mixer against a transition piece. The external teeth and the internal toothed grooves of the bolt fixing apparatus are engaged with each other to stop the rotation of the beam bolt.
The conventional installation of a jet pump beam did not allow direct checking of the installation condition of the jet pump beam to the transition piece (pushing force to the elbow by the jet pump beam, and presence of a foreign object between the insert member and a lower end of the beam bolt) during the jet pump beam installation. If the pushing force to the elbow by the jet pump beam is not enough or if a foreign object is caught between the insert member and the end of the beam bolt, it may cause vibration of the inlet mixer due to insufficient pushing force to the elbow for resisting upward force exerted by a flowing fluid, and the jet pump may not function as assumed.
Additionally, methods for checking bolt installation are stated, for example, in Japanese Patent Laid-open No. 2(1990)-88127, Japanese Patent Laid-open No. 2(1990)-304325, and Japanese Patent Laid-open No. 3(1991)-214033.
Japanese Patent Laid-open No. 2(1990)-88127 states a screw seating confirming apparatus. This screw seating confirming apparatus has an ultrasonic sensor installed inside a holder, an ultrasonic pulse generator for sending ultrasonic waves to the ultrasonic sensor, a receiver for receiving echo signals from the ultrasonic sensor, and a gate circuit for inputting each output signal from the receiver and the ultrasonic pulse generator to detect a level of voltage of echo from a seating surface of the object for installing a screw tightening unit where a head portion of the screw tightening unit comes in contact with. In the screw seating confirming process stated in Japanese Patent Laid-open No. 2(1990)-88127, it is focused attention on the following aspects: when the screw tightening unit is seated to the target object, compared to when it is not seated, a reflection rate of the ultrasonic waves at the seating surface of the object is decreased and a level of echo voltage of the same is reduced.
Japanese Patent Laid-open No. 2(1990)-304325 states a method for confirming bolt clamping operation using ultrasonic wave. In this method for confirming bolt clamping operation, a clamped state of a bolt is confirmed by setting a gate for each location of reflection echoes and taking the absolute value of a difference between a pre-stored reference value of a reference bolt and a measured value of a measuring bolt, or by taking a ratio of the pre-stored reference value to the measured value.
Further, Japanese Patent Laid-open No. 3(1991)-214033 states a technology for measuring an axial tension and bending of a bolt based on propagation time and the echo height of ultrasonic waves before and after bolt tightening.